Easy, just breed water and dark dragons
carnivore+storm=petroleum dragon
in to a breedin
what can you get a legendary dragon will breed
petroleum and water
zombie + mud
pirate or petroleum dragon
i breed a nenufar dragon and neon dragon,and i get a petroleum dragon.
water+ dark
petroleum waterfal
its easy water+dark
you can breed some legendary Pokemon with ditto but the rest you cant
breed a water and dark,, you can also breed nenufar and neon and get it and be happy :P